1. Field of the Invention
The present invention relates to a thin film transistor, a method of fabricating the same and an organic light emitting diode (OLED) display device having the same.
2. Description of the Related Art
Generally, a polycrystalline thin film transistor used in a display device is fabricated by depositing amorphous silicon on a transparent substrate formed of glass or quartz, dehydrogenating the amorphous silicon, and crystallizing the amorphous silicon to form a semiconductor layer. After that, a gate insulating layer and a gate electrode are formed on the semiconductor layer, an impurity is injected into the semiconductor layer to form source and drain regions, and an interlayer insulating layer and source and drain electrodes are formed, so that the thin film transistor is completed.
Alternatively, to improve electrical characteristics of a thin film transistor, channel doping may be further performed. To be more specific, after injecting a predetermined impurity into a semiconductor layer, ion-injection for improving electrical characteristics of a region to be a channel, i.e., channel doping is performed, and then a gate insulating layer and a gate electrode are formed on the semiconductor layer.
However, in a common process of fabricating the thin film transistor, an annealing process for activating impurity ions injected into the semiconductor layer has to be performed after the channel doping. Therefore, the process becomes complicated and production yield is lowered.
A gate insulating layer insulating the semiconductor layer is generally formed of silicon oxide or silicon nitride by chemical vapor deposition (CVD). However, the layer deposited by CVD has poor quality and uniformity, so that the layer has to be deposited to a thickness of 1000 Å (angstroms) or more.
Examples of thin film transistors are found in commonly assigned co-pending patent application Ser. No. 11/987,951 filed 6 Dec. 2007 and published on 12 Jun. 2008 having Publication No. 2008/0135893 entitled “Thin Film Transistor, Method of Fabricating the Same, and Display Device Including the Same” to Hye-Hyang Park et al., and commonly assigned co-pending patent application Ser. No. 11/951,525 filed 6 Dec. 2007 and published on 12 Jun. 2008 having Publication No. 2008/0135838 entitled “Thin Film Transistor, Method of Fabricating the Same, and Organic Light Emitting Diode Display Device Including the Same” to Hye-Hyang Park.
For this reason, the electrical characteristics of the thin film transistor are difficult to be controlled, and overall characteristics of the thin film transistor become degraded.